As disclosed by Japanese Patent No. 3447191 and JP-A-2001-286260, known techniques for increasing the natural umami (favorable taste, savoriness and/or taste with fullness) components of tea drinks comprise dipping tea leaves in water while controlling temperature, pressure or dipping time to thereby optimize an efficiency of extracting the water-soluble natural umami components contained in the tea leaves.
According to Shin Sagyo Zensho, 8th ed., 1988 (Chamber of Tea Association of Shizuoka Pref.), however, the content of water-soluble components of tea leaves is restricted to about 40%. Therefore, only a limited amount of the natural umami components can be obtained by the above-described methods. In recent years, therefore, there has been proposed a method comprising blending finely ground tea leaves with a tea extract to thereby impart natural umami components of tea leaves that have thus far not been utilized since they are not soluble in water, as disclosed in PCT/JP2004/008349. However, this method suffers from a disadvantage that since the natural umami components are not dissolved but taken as solids, the drink has a powdery or coarse (heavy) texture which impairs a pleasant refreshing mouth feel of tea. Recently, attempts have been also made to increase natural umami components in a tea extract by enzymatically treating tea leaves with, for example, cellulase or protease and thus making water-insoluble components soluble in water, as disclosed by Japanese Patent No. 3157539.
As an example of the methods of making water-insoluble components soluble in water by using an additive that is employed in different fields, Japanese Patent No. 3435492 discloses a technique of solubilizing cellulose in water by using a formic acid/calcium chloride based medium. In a case where water-insoluble components are made soluble in water by adding such substances, however, the substances other than tea leaves and water affect the flavor. Therefore, these methods are seemingly not adequate for effectively drawing out natural umami components.
Recently, there are increasing needs for tea-based alcoholic drinks. It is required that a tea-based alcoholic drink has a rich tea leaf-origin aroma. When provided as packed beverages, it is possible to easily have these tea-based alcoholic drinks anytime.
To extract the aroma components into a drink, there have been proposed various techniques. For example, JP-A-2002-209519 discloses an alcohol extraction method focusing on the fact that most of the aroma components are fat-soluble. JP-A-2003-225053 discloses a cold water extraction method for solving the problems caused by heating, for example, browning of an extract, impairment of a fresh aroma, loss of a fresh tea leaf-like aroma due to increased astringency caused by extraction of catechins in a large amount. By combining these techniques, furthermore, it becomes possible to obtain a tea-based alcoholic drink which contains the aroma components in a large amount, suffers from no thermal denaturation at the extraction step and sustains the rich tea leaf-origin aroma.
Although tea-based alcoholic drinks manufactured by these methods have an outstanding tea leaf-origin aroma, they are still insufficient in umami of tea or body and have considerable alcoholic stimulation as an aftertaste. From the viewpoint of overall qualities, therefore, these products still suffer from problems to be overcome in flavor balance including the aftertaste.
To improve the body of a food or a drink and mask a stimulative smell, seasonings and additives containing peptides have been marketed in these days. However, most of these peptides are obtained by enzymatically treating starting materials such as fishes and cereals. Thus, there is a concern that these seasonings or additives will impair the tea flavor that is the primary characteristic of tea-based drinks. Accordingly, it has been desired to develop a tea-based alcoholic drink which has a “tea leaf-origin aroma”, “umami and body” and “mild alcoholic aftertaste” in a good balance.